Category: Class 12 Biology

NCERT  Solutions For Class 12 Biology Biotechnology: Principles And Processes

Topics and Subtopics in NCERT Solutions for Class 12 Biology Chapter 11 Biotechnology: Principles And Processes:

Section Name	Topic Name
11	Biotechnology:Principles And Processes
11.1	Principles of Biotechnology
11.2	Tools of Recombinant DNA Technology
11.3	Processes of Recombinant DNA Technology
11.4	Summary

QUESTIONS FROM TEXTBOOK SOLVED

1. Can you list 10 recombinant proteins which are used in medical practice? Find out where they are used as therapeutics (use the internet).
Ans: (i) Human insulin – Diabetes
(ii) Human growth hormone – Dwarfism cure
(iii) Blood clotting factor Y1H/IX-Haemophilia
(iv) TPA (tissue plasminogen activator) – Heart attack/strokes
(v) PDGF (platelet derived growth factor) – Stimulates wound healing.
(vi) Interferon – Treatment of viral infection.
(vii) Interlinking – Enhances immune reaction,
(viii) Hepatitis B vaccine – Prevention of infectious disease.
(ix) Herpes Vaccine – Prevention of infectious disease.
(x) DNase I – Treatment of cystic fibrosis.

2. Make a chart (with diagrammatic representation) showing a restriction enzyme, the substrate DNA on which it acts, the site at which it cuts DNA and the product it produces.
Ans: Name of the Restriction enzyme – Bam HI.
The substrate DNA on which it acts –

3. From what you have learnt, can you tell whether enzymes are bigger or DNA is bigger in molecular size? How did you know?
Ans: Both DNA (deoxyribonucleic acid) and enzymes are macromolecules. DNA is a polymer of deoxyribonucleotides and enzymes are proteins hence these are polymers of amino acids. But DNA is bigger in molecular size as compared to proteins because synthesis of proteins is regulated by a small segment of DNA, called genes and also a large number of proteins can be synthesised by a DNA molecule.

4. What would be the molar concentration of human DNA in a human cell? Consult your teacher.
Ans: The molar concentration of DNA in human cell is 2 mg/ml of cell extract.

5. Do eukaryotic cells have restriction endonucleases? Justify your answer.
Ans: No, eukaryotic cells do not have restriction endonuclease because DNA molecules of eukaryotes are heavily methylated. All the restriction endonucleases have been isolated from various strain of bacteria.

6. Besides better aeration and mixing properties, what other advantages do stirred tank bioreactors have over shake flasks?
Ans: Shake flasks are used for growing and mixing the desired materials on a small scale in the laboratory. A large scale production of desired biotechnological product is done by using ‘bioreactors’. Besides better aeration and mixing properties, the bioreactors have following advantages
(i) Small volumes of cultures are periodically withdrawn from die reactor for sampling.
(ii) It has a foam control system, pH control system and temperature control system.
(iii) Facilitates even mixing and oxygen availability throughout the bioreactor.

7. Collect 5 examples of palindromic DNA sequences by consulting your teacher. Better try to create a palindromic sequence by following base-pair rules.
Ans: Palindrome nucleotide sequences in the DNA molecule are groups of bases that form the same sequence when read both forward and backward. Five examples of palindromic DNA sequences are as follows:
(i) 5′-—————GGATCC——————3’
3′—————CCTAGG—————–5′
(ii) 5’—————AAGCTT——————3′
3′——————TTCGAA —————-5′
(iii) 5′—————–ACGCGT—————–3′
3′——————TGCGGA————– 5′
(iv) 5′———- ACTAGT————3′
3′——————TGATCA————5′
(v) 5′—————AGGCCT—————3′
3′——————TCCGGA————–5′

8. Can you recall meiosis and indicate at what stage a recombinant DNA is made?
Ans: Recombinant DNA is formed due to crossing over between non-sister chromatids of homologous chromosome. It occurs during pachytene stage of prophase of meiosis I

9. Can you think and answer how a reporter enzyme can be used to monitor transformation of host cells by foreign DNA in addition to a selectable marker?
Ans: A reporter enzyme can be used to differentiate transformed cells by tracking down the activity of its co-responding genes (receptor gene). For e.g., (3-galactosidase (Lac Z) activity is not found in transformed cells so that they appear white in colour. The others, which appear blue in colour, indicate that cells do not carry foreign DNA.

10. Describe briefly the followings:
(a) Origin of replication
(b) Bioreactors
(c) Downstream processing
Ans: (a) Origin of Replication: This is a sequence from where replication starts and any piece of DNA when linked to this sequence can be made to replicate within the host cells. This sequence is also responsible for controlling the copy number of the linked DNA. So, if one wants to recover many copies of the target DNA it should be cloned in a vector whose origin support high copy number.

(b) Bioreactor: Bioreactors can be thought of as vessels in which raw materials are biologically converted into specific products by microbes, plant and animal cell and/or their enzymes. The bioreactor provides optimum growth conditions and facilitates achieving the desired products. The most commonly used bioreactor is of stirring type. A stirred tank bioreactor is usually a cylindrical vessel or vessel with a curved base to facilitate mixing of the contents. In the sparged stirred tank bioreactor, sterile air bubbles are sparged. The stirrer facilitates the mixing and oxygen availability throughout the bioreactor. A bioreactor has an agitator system, an oxygen delivery system, a foam control system, a temperature control system, pH control system and sampling ports.

(c) Downstream Processing : The product obtained is subjected to a series, of processes collectively called downstream processing before it is made into a finished product ready for marketing. The two main processes are separation and purification. The product is then formulated with suitable preservatives. Such formulations have to undergo clinical trials, in case of drugs.

11. Explain briefly
(a) PCR
(b) Restriction enzymes and DNA
(c) Chitinase
Ans: (a) PCR = Polymerase chain reaction (in vitro method) is a molecular biological technique for enzymatically replicating DNA without using a living organism, such as E. coli or yeast.
3 steps in PCR are –
(i) Denaturation of desired double strand DNA-to ssDNA.
(ii) Annealing of primer to ssDNA (single standard).
(iii) Extension of primer by Taq DNA polymerase isolated form Thermits aquaticus.
Uses – Amplification of desired gene/gene cloning.
Advantage- More output, greater efficiency, less error prone, less human interference and cyclic and automated.
(b) Restriction enzymes and DNA – Restriction enzymes is a group of enzymes used to cleave or cut DNA strands each having a characteristics base sequence at which it cleaves.
(i) It restricts foreign DNA from entering normal cell by digesting it at various recognition site. Recognition site is palindromic.
(ii) They are endonuclease and exonuclease both types.
(iii) They produces sticky ends. Cleavage site and recognition site are different from each other. Restriction enzymes therefore are believed to be a mechanism evolved by bacteria to resist viral attack and to help in the removal of viral sequences.
(c) Chitinase – Chitinase is a enzyme to digest or breakdown glycosidic bonds in chitin cell wall of fungal cell to facilitate its transformation.

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NCERT Solutions For Class 12 Biology Biodiversity and Conservation

Topics and Subtopics in NCERT Solutions for Class 12 Biology Chapter 15 Biodiversity and Conservation:

Section Name	Topic Name
15	Biodiversity and Conservation
15.1	Biodiversity
15.2	Biodiversity Conservation
15.3	Summary

QUESTIONS FROM TEXTBOOK SOLVED

1. Name the three important components of  biodiversity.
Ans: Three components of biodiversity are:
(a) Genetic diversity
(b) Species diversity
(c) Ecological diversity

2. How do ecologists estimate the total number of species present in the world?
Ans: Ecologists estimate the total number of species present in the world by comparing species richness of some exhaustively studied groups between any two regions (tropics, temperate or polar regions). Species richness, as a measure of diversity, has been used by many ecologists. Species density or the number of species per m² is most commonly used to measure species richness. Species abundance and species proportional abundance based indices are some other alternative approaches to the measurement of diversity.

3. Give three hypothesis for explaining why tropics ’”show greatest levels of species richness.
Ans: (1) The tropical area have a more stable climate than temperate zones. Local species continues to live in absence of natural disturbances.
(2) Warm temperature and high humidity in most tropical areas provide favourable conditions for growth and survival of diverse species.
(3) Tropical areas receive more solar energy over year and thus tropical communities are more productive and can support a wide range of species.

4. What is the significance of the slope of regression in a species-area relationship?
Ans: Slope of regression or regression coefficient makes it easier to measure species richness along an area. For a limited area like, a country, it gives a constant value of 0.1 to 0.2 irrespective of the taxonomic group or region. It remains amazingly similar for all those small regions. On the contrary, for measuring species-area relationship over large areas like the entire continents, the slope of regression values in the range of 0.6 to 1.2.

5. What are the major causes of species losses in a geographical region?
Ans: Species are lost in a geographical region due to natural disturbances like forest fires; famine, drought and also due to human disturbance with over replantation, habitat destruction, habitat displacement, over specialization, intensive agriculture and pollution.

6. How is biodiversity important for ecosystem functioning?
Ans: Biodiversity is important for ecosystem functioning because,
(1) It contributes to productivity.
(2) It cause more efficient recycling of energy and matter.
(3) It has many alternative pathways for survival under diverse conditions.
(4) Rich biodiversity provides alternatives available at each trophic level. All organisms are linked in food chains and interact with their abiotic environment in such a way so as to keep the natural cycles going and make the ecosystems self – sustaining units. Disappearance of any link in a food chain will not affect the ecosystem as other alternatives are there.

7. What are sacred groves? What is their role in conservation?
Ans: Sacred forests or sacred groves are forest patches around places of worship which are held in high esteem by tribal communities. They are the most undisturbed forest patches which are often surrounded by highly degraded landscapes. They are found in several parts of India, e.g., Karnataka, Maharashtra, Rajasthan (Aravalli), Madhya Pradesh (Sarguja, Bastar), Kerala, Meghalaya. Temples built by tribals are found surrounded by deodar forests in Kumaon region, Jaintias and Khasjas in Meghalaya. Not a single branch is allowed to be cut from these forests. As a result many endemic species which are rare or have become extinct elsewhere can be seen to flourish here. Bishnois of Rajasthan protect Prosopis cineraria and Black Buck religiously. Some water bodies are also held sacred in certain places, e.g., Khecheopalri in Sikkim. Their aquatic flora and fauna are naturally preserved.

8. Among the ecosystem services are control of floods and soil erosion. How is this achieved by the biotic components of the ecosystem?
Ans: Ecosystem services are products or benefits given by ecosystem processes to the environment for its purification, beauty, biodiversity, protection of natural resources, habitat to wild life and tribals, protection of soils, CO₂ – O₂ balance, retention of water against floods, drought and pollution. Plants play a vital role in the control of floods and soil erosion. Their roots bind the soil 10. particles firmly and in this way they do not allow the top soil to be drifted away by winds or moving water. Roots of plants also make the soil porous and allow water to go into the soil.

9. The species diversity of plants (22 per cent) is much less than that of animals (72 per cent). What could be the explanations to how animals achieved greater diversification?
Ans: Species diversity refers to the variety of species within a region which is less in plants as compared to animals. It is due to greater dispersal/more number of surviving individuals. Most animals possess simple or complex nervous system to control and coordinate various activities. They possess receptors to receive against them. Most of their responses are adaptive and ensure their survival in changing environmental conditions. They, therefore, have evolved to reveal much higher species diversity than plants who do not possess nervous system and respond differently against environment stimuli.

10. Can you think of a situation where we deliberately want to make a species extinct? How would you justify it?
Ans: Humans can cause extinction of species through various means. We are trying to eradicate disease causing organisms (e.g., poliovirus) from this world to make this world disease free. Since such micro-organisms are harmful to the human society, such attempt is justified. Further, such micro-organisms are not essential components (producers or decomposers) of any ecosystem, and losing one or few such organisms would not affect the functioning of ecosystem.

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NCERT Solutions For Class 12 Biology Organisms and Populations

Topics and Subtopics in NCERT Solutions for Class 12 Biology Chapter 13 Organisms and Populations:

Section Name	Topic Name
13	ORGANISMS AND POPULATIONS
13.1	Organism and Its Environment
13.2	Populations
13.3	Summary

QUESTIONS FROM TEXTBOOK SOLVED

1. How is diapause different from hibernation?
Ans: Diapause is a period of suspended growth or development occuring in many insects and other invertebrates during which metabolic activities are greatly reduced. On the other hand, hibernation is a sleep like state in which a few animals, such as fishes and amphibians, pass the winter season as a way of surviving food scarcity and cold weather.

2. If a marine fish is placed in a fresh water aquarium, will the fish be able to survive? Why or why not?
Ans: When a marine fish is placed in a fresh water aquarium, the fish will not be able to survive because marine fish is adapted to live in saline seawater. In fresh water, it will not be able to cope with the outside hypotonic environment because of osmoregulation problem. In fresh water, the concentration of water, the difference between the concentration of the water and inside of the fish are increased and therefore, the osmotic pressure is also increased.The fish has to take more water into the body to be able to survive and to get rid of the excess salt present in its body.

3. Define phenotypic adaptation. Give one example.
Ans: Phenotypic adaptations are non-genetic changes
occurring in living organisms due to various extreme environmental conditions, such as stress, extreme temperature, change of habitat. These includes acclimatization, behavioural changes, etc.

4. Most living organisms cannot survive at temperature above 45°C. How are some microbes able to live in habitats with temperatures exceeding 100°C?
Ans: Micro-organisms of hot.springs and vents (mouth of sea bed volcanoes) are able to survive at the high temperature due to
(i) occurrence of branched chain lipids in their cell membrane that reduce fluidity of cell membranes.
(ii) having minimum amount of free water in their bodies. Removal of water provides resistance to high temperature.

5. Last the attributes that populations but not individuals possess.
Ans: Some significant attributes that populations but not individual possess are –
(i) Natality
(ii) Mortality
(iii) Growth forms
(iv) Population density
(v) Population dispersion
(vi) Population age distribution
(vii) Sex ratio

6. If a population growing exponentially double in size in 3 years, what is the intrinsic rate of increase (r) of the population?
Ans: If the population growing exponentially double in size in 3 years, the intrinsic rate of increase of this population will be towards maximum.

7. Name important defence mechanisms in plants against herbivory.
Ans: There are various defence measures for animals against predators. But plants, as they cannot move away, have certain defence mechanisms against herbivory. Their main defences are chemical toxins, such as strychnine, a poison produced by tropical vine, morphine by opium poppy, nicotine produced by tobacco plant. Apart from these chemicals, the common defence measure is presence of spines (modified leaves) on the leaves, stems of the plant, modifications of leaves into thorns, development of sharp silicated edges in leaves which prevent them against damage caused by herbivores.

8. An orchid plant is growing on the branch of mango tree. How do you describe this interaction between the orchid and the mango tree?
Ans: An orchid plant is growing on the branch of a mango tree is called epiphyte, i.e., plants growing on other plants or trees. This type of interaction is known as commensalism, where in orchid / derives benefit of interaction whereas mango tree is not affected. The orchid growing on the branch of mango tree get more light to grow and also, the mango is not harmed in any way.
Commensalism can be defined as an interaction between two animal or plant species that habitually live together in which one species benefits from the association while the other is not significantly affected.

9. What is the ecological principle behind the biological control method of managing with pest insects?
Ans: The ecological principle behind the biological control method of managing with pest insects is predator – prey relationship. It is based on the ability of the predator to regulate prey population.

10. Distinguish between the following:
(a) Hibernation and Aestivation
(b) Ectotherms and Endotherms
Ans:

11. Write a short note on
(a) Adaptations of desert plants and animals
(b) Adaptations of plants to water scarcity
(c) Behavioural adaptations in animals
(d) Importance of light to plants
(e) Effect of temperature or water scarcity and the adaptations of animals.
Ans: (a) Desert plants have very small leaves or no leaves at all, and carrying out photosynthesis through the stems. Their stem could become succulent, and can store and retain water. Animals living in hot climatic region tend to be smaller than those living in cold climates. This can be explained by the fact that the amount of heat gained from the environment is approximately proportional to the body surface area. The majority of animals living in desert are small, like kangaroo rat. It feed on dry seeds and other dry plant material and does not drink,

(b) The evergreen trees such as Rhododendron, show water scarcity by an inward curling of the leaves. A more significant response is the closure of stomata, which reduces transpiration, but raises the internal temperature of die leaf affecting the rate of synthesis of proteins and photosynthesis. Deciduous trees of the temperature region drop their leaves in autumn, avoiding winter drought. Some water stressed plant’s accumulate excessive amounts of inorganic ions.

(c) Migrating temporarily to a less stressful habitat forms a more stressful habitat is a kind of behavioural adaptation in animals which enables them to survive in better environmental conditions. Desert lizards regulate their body temperature constant by behavioural means. They bask in the sun and absorb heat when their body temperature decreases below the optimum, but move into shady or underground places when the temperature of the surrounding area starts increasing.

(d) Light affects plants through its quality, intensity and duration. Duration of light affects phenology, photosynthesis, growth, reproduction, flowering. Quality of light influences flowering, seed germination and movements. Light is required for the production of chlorophyll in chloroplasts. Plants germinated under insufficient illumination causes the destruction of chlorophyll.

(e) Animals mainly are of two types as they are adapted to controlling their body temperature. Poikilothermous are the animals whose temperature fluctuates with that of the environment, e.g., invertebrates and vertebrates, other than birds and animals. In contrast, homeotherms are the animals which can maintain their body temperature at a constant level, e.g., birds and mammals.

12. List the various abiotic environmental factors.
Ans: Abiotic factors are non living factors and conditions of the environment which influence survival, function and behaviour of organisms. Various abiotic factors are :

(i) Temperature – Temperature is one of the most important environmental factors. The average temperature varies seasonally. It ranges from subzero level in polar areas and high altitudes to more than 50°C in tropical deserts in summer and exceeds 100°C in thermal springs and deep-sea hydrothermal vents.

(ii) Water – Next to temperature, water is the most important factor which influences the life of organisms. The productivity and distribution of land plants are dependent upon availability of water. Animals are adapted according to the water availability. E.g., aquatic animals are ammonotelic while xerophytic animals excrete dry feces and concentrated urine.

(iii) Light – Plants produce food through photosynthesis for which sunlight is essential source of energy. Light intensity, light duration and light quality influences the number of life processes in organisms, such as – photosynthesis, growth, trans-piration, germination, pigmentation, movement and photoperiodism.

(iv) Humidity – Humidity refers to the moisture (water vapour) content of the air. It determines the formation of clouds, dew and fog. It affects the land organisms by regulating the loss of water as vapour from their bodies through evaporation, perspiration and transpiration.

(v) Precipitation – Precipitation means rainfall, snow, sleet or dew. Total annual rainfall, seasonal distribution humidity of the air and amount of water retained in the soil are the main criteria that limit the distribution of plants and animals on land.

(vi) Soil – The soil is one of the most important ecological factor called the edaphic factor. It comprises of different layers called horizons. The upper weathered humus containing part of soil sustains terrestrial plant life.

13. Give an example for:
(a) An endothermic animal
(b) An ectothermic animal
(c) An organism of the benthic zone
Ans: (a) Man, (Homo sapiens)
(b) Black bear
(c) Corals

14. Define population and community.
Ans: Population can be defined as the total number of individuals of a species or any other class of an organism in a defined area or habitat or a group of individuals of the same species within a commnity.
Community can be defined as a naturally octurring assemblage of species living within a defined area or habitat.

15. Define the following terms and give one example for each:
(a) Commensalism
(b) Parasitism
(c) Camouflage (d)Mutualism
(e) Interspecific competition
Ans: (a) Commensalism is the association between organisms of different species in which one species benefits but does not apparent harm to the other. For example, in the large intestine of human being, bacteria Escherichia coli are present which helps in digestion.
(b) Parasitism is an association in which one organism lives on or in the body of another, from which it obtains its food. For example, the parasites of humans include fleas and lice, various bacteria, protozoans and fungi.
(c) Camouflage is a high degree of similarity between an animal and its visual environment, which enables it be disguished or concealed. For example, birds with necks and heads of contrasting colours are not easily recognised by their enemies under certain conditions.
(d) Mutualism is an association between two organisms of different species in which each partner benefits. For example, the cross fertilization or pollination of plant flowers by insects (sometimes by birds) is a mutual relation of wide occurrence and great importance, because many plants are self- sterile.
(e) Inter-specific competition can be defined as an interaction occurs between different species that share some environmental resource when this is in short supply. Inter-specific competition often results in the dominance of one species over another. For example, when two species of Paramoecium,Paramoecium caudatum and P.aurelia are confined in a closed containers with fixed amount of food, out of them one species always died out.

16. With the help of suitable diagram describe the . ; logistic population growth curve.
Ans: The S-shaped growth curve is also called a logistic growth curve. It describes a situation in which (in a new environmental condition) the population density of an organism increases slowly establishing itself then increasing rapidly, approaching an exponential growth rate. Many population of micro-organisms broadly follow this basic sigmoidal pattern. For example, when a fresh culture medium is inoculated with bacteria, sigmoidal or S-shaped growth curve is observed. The S-shaped curve is generated when a population approaches the environmental’s carrying capacity. Carrying capacity is the maximum number of individuals of a population that can be supported in a given time.

The S-shaped growth form is represented by the following equation- ” dNldt = rN[K-NIK]
Where, r = intrinsic rate of natural increase N = population density at time t K = carrying capacity

17. Select the statement which explains best parasitism.
(a) One organism is benefited.
(b) Both the organisms are benefited.
(c) One organism is benefited, other is not affected.
(d) One organism is benefited, other is affected.
Ans:(d) One organism is benefited, other is affected.

18.List any three important characteristics of a population and explain.
Ans: The three important characteristics of a population are:
(a) Density: The number of individuals per unit area or volume. For example, the number of frogs per m³ of forest region.
(b) Natality or Birth rate: The birth rate is determined by the number of individuals bom to a given population during a given period of time.
(c) Mortality or Death rate: The death rate or mortality represents a decrease in a given population during a given period of time. Generally, the death of individuals in a population are expressed by specific mortality which is described as the mortality population are expressed by specific mortality which is described as the mortality for given age group.

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NCERT Solutions For Class 12 Biology Biotechnology and its Applications

Topics and Subtopics in NCERT Solutions for Class 12 Biology Chapter 12 Biotechnology and its Applications:

Section Name	Topic Name
12	Biotechnology and its Applications
12.1	Biotechnological Applications in Agriculture
12.2	Biotechnological Applications in Medicine
12.3	Transgenic Animals
12.4	Ethical Issues
12.5	Summary

QUESTIONS FROM TEXTBOOK SOLVED

1. Crystals of Bt toxin produced by some bacteria do not kill the bacteria themselves because –
(a) bacteria are resistant to the toxin
(b) toxin is immature;
(c) toxin is inactive;
(d) bacteria encloses toxin in a special sac.
Ans: (c) Toxin is inactive.

2. What are transgenic bacteria? Illustrate using any one example.
Ans: Bacteria having gene or genes usually from an unrelated organism incorporated into their genome are called transgenic bacteria. For example, when human insulin gene is introduced into the isolated plasmid of E.coli bacterium and this recombinant DNA is transferred into a fresh bacterium, then the later is said to be transgenic or transformed bacterium.

3. Compare and contrast the advantages and disadvantages of production of genetically modified crops.
Ans:

4. What are Cry proteins? Name an organism that produces it. How has man exploited this protein to his benefit?
Ans: The bacterium Bacillus thuringiensis is a common soil bacterium which produces a protein toxin that kills certain insects. The toxin is a crystal (Cry) protein. There are several kinds of Cry proteins which are toxic to different groups of insects. The gene encoding Cry protein is called cry gene. Biotechnologists have been able to isolate the gene responsible for production of toxin and to introduce it into a number of plants to produce genetically modified plants resistant to insects, e.g., Bt cotton (resistant to bollworm) and GM tobacco (resistant to hornworms).

5. What is gene therapy? Illustrate using the example of adenosine deaminase (ADA) deficiency.
Ans: Gene therapy is correction of malfunctioning/gen by repairing or adding correct copy. ADA (adenosine deaminase deficiency) is a very rare genetic disorder due to deletion of the gene for adenosine deaminase. The enzyme is crucial for the immune system to functions. It can be treated by gene therapy. This gene is transfected into early embryonic cells of bone marrow for permanent use.

6. Digrammatically represent the experimental steps in cloning and expressing an human gene (say the gene for growth hormone) into a bacterium like E. coli?
Ans:

7. Can you suggest a method to remove oil (hydrocarbon) from seeds based on your understanding of rDNA technology and chemistry of oil?
Ans: The genes for the formation of oil in the seed should be identified. The appropriate genes should be removed with the help of restriction endonucleases. Such DNA should then be treated with DNA ligases to make seal DNA at the broken ends. These cells when grown aseptically on nutrient medium will differentiate into a new plant whose seeds will not have oil in them.

8. Find out from internet what is golden rice.
Ans: Golden rice is a transgenic variety of rice (Oryza sativa) containing good quantities of β-carotene (provitamin A) which is principle source of vitamin A. Since the grains of the rice are yellow in colour due to β-carotene, the rice is commonly called golden rice. It was developed at Swiss Federal Institute of Technology by Professor Ingo Potrykus and Peter Beyer.

9. Does our blood have proteases and nucleases?
Ans: No, blood does not have protease and nuclease. If it would have been there blood and cell would have been digested, some protease do exist in inactive form.

10. Consult internet and find out how to make orally activ&protein pharmaceutical. What is the major problem to be encountered?
Ans: Orally active protein product that is successfully manufactured is vaccines for preventions of infectious diseases such as hepatitis B, herpes, influenza, etc. Gene for antigen are isolated from bacteria and grown along with cut leaf portions of potato plant in antibiotic medium – followed by callus formation and recombinant/transgenic potato are obtained which contain those vaccines.

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NCERT Solutions For Class 12 Biology Microbes in Human Welfare

Topics and Subtopics in NCERT Solutions for Class 12 Biology Chapter 10 Microbes in Human Welfare:

Section Name	Topic Name
10	Microbes in Human Welfare
10.1	Microbes in Household Products
10.2	Microbes in Industrial Products
10.3	Microbes in Sewage Treatment
10.4	Microbes in Production of Biogas
10.5	Microbes as Biocontrol Agents
10.6	Microbes as Biofertilisers
10.7	Summary

QUESTIONS FROM TEXTBOOK SOLVED

1. Bacteria cannot be seen with the naked eyes, but these can be seen with the help of a microscope. If you have to carry a sample from your home to your biology laboratory to demonstrate the presence of microbes under a microscope, which sample would you carry and why?
Ans: Soil sample/water sample as they are the natural habitat of micro-organisms and can be directly observed.

2. Give examples to prove that microbes release, gases during metabolism.
Ans: There are lots of examples which prove, that microbes release gases during their metabolism. Some examples are as follows :

• Dough, which is used for making dosa and idli is fermented by bacteria. The puffy appearance of dough is due to production of CO₂ by fermentation process.
• Swiss cheese is characterized by having the characteristic flavour and large holes. The large holes are formed due to the amount of CO₂ released by a bacterium Propionibacterium sharmanii.

3. In which food would you find lactic acid bacteria? Mention some of their useful applications.
Ans: Milk, Curd and Cheese are coagulated product. Lactic acid bacteria (LAB) convert lactose sugar into lactic acid. They also improve the nutritional quality of curd by increasing vitamin B₁₂. Lactic acid bacteria are also found in the stomach where they check disease causing microbes.

4. Name some traditional Indian foods made of wheat, rice and Bengal gram (or their products) which involve use of microbes.
Ans: A number of dishes can be prepared through fermentation process by using microbes. Some important traditional dishes made up of wheat, rice and Bengal gram or black gram (vernacular urad) are as follows :

• Bread – It is a fermented preparation of wheat by Saccharomyces cerevisiae.
• Dosa, upma and idli – They are fermented preparation of rice and black gram (urad). The two are allowed to ferment for 3-12 hrs with Leuconostoc and Streptococcus species of bacteria.

5. In which way have microbes played a major role in controlling diseases caused by harmful bacteria?
Ans: By production of antibiotics like penicillin, tetracyclin, by production of vaccines for herpes, TB, DPT, etc.

6. Name any two species of fungus, which are used in the production of the antibiotics.
Ans: Penicillium chrysogenum, P. notatum, produce penicillin and Cephalosporium produces cephalosporins.

7. What is sewage? In which way can sewage be harmful to us?
Ans: Sewage is waste water release from household and industrial applications. It is harmful as
(i) it decreases flora mid fauna of H₂O.
(ii) contamination of H₂O/food/soil.
(iii) dissemination of pathogenic bacteria.

8. What is the key difference between primary and secondary sewage treatment?
Ans: There are three stages of sewage treatment : primary, secondary and tertiary. Primary treatment is a physical process while secondary is a biological process and tertiary is a chemical process.

9. Do you think microbes can also be used as source of energy? If yes, how?
Ans: Yes, the microbes present in activated sludge are digested anaerobically to generate a biogas i.e. by release of inflammable biogas in biogas plant, which is a source of energy.
Use of microbial culture for SCP (single cell protein).

10. Microbes can be used to decrease the use of chemical fertilizers and pesticides. Explain how this can be accomplished.
Ans: Microbes can be used to decrease the use of chemical fertilizers and pesticides. This can be accomplished by the use of biofertilizers. The main source of biofertilizers are bacteria, fungi and cyanobacteria. They can provide plant nutrients at cheaper cost when compared with the chemical fertilizers. e.g.
(i) Use of leguminous plant with Rhizobium.
(ii) Use of sulphur fixing bacteria.
(iii) Use of hydrogen fixing bacterium.

11. Three water samples namely river water, untreated sewage water and secondary effluent discharged from a sewage treatment plant were subjected to BOD test. The samples were labelled A, B and C; but the laboratory attendant did not note which was which. The BOD values of the three samples A, B and C were recorded as 20 mg/L, 8 mg/Land 400 mg/L, respectively. Which sample of the water is most polluted? Can you assign the correct label to each assuming the river water is relatively clean?
Ans: The sample with BOD value of 400 mg/h is most polluted and should be levelled as B —> untreated sewage river H₂O will be —> less BOD —> 8 mg/L – sample A.
Untreated water —> 2° effluent BOD —>River water 400 —> 20 —> 8 and so should be labelled as sample C.

12. Find out the name of the microbes from which cyclosporin A (an immuno suppressive drug) and statins (blood cholesterol lowering agents) are obtained.
Ans: Cyclosporin A (an immuno suppressive drug) is obtained from fungus Trichoderma polysporum while statins (blood cholesterol lowering agent) is obtained from yeast Monascus purpureus.

13. Find out the role of microbes in the following and discuss it with your teacher.
(a) Single cell protein (SCP)
(b) Soil
Ans: SCP – single cell protein is microbial yield/cell crop of bacterial, yeast, algae rich in protein. The protein content of microbial cell is very high. Dried cell of Pseudomonas grown on petroleum product has 69% protein and these proteins have all essential amino acids.

Soil : Microbes take part in formation and maintenance of soil. They add organic matter to freshly formed soil. The process is called humification. Some microbes act as biofertilizers and biopesticides.

14. Arrange the following in the decreasing order (most important first) of their importance, for the welfare of human society. Give reasons for your answer.Biogas, Citric acid, Penicillin and Curd.
Ans: Curd: Less important for society – as it depends on individual use and has only nutritions value.
Citric acid : Industrial use, not for dissipation in community.
Penicillin: Medicinal use of microbes, good for health of society, commercially more usable.
Biogas: Most important for community welfare as
(i) it reduces excreta, waste from community.
(ii) it produces inflammable gases, can be used as energy source.
(iii) it is a renewable source.
(iv) it has multidimensional utility.
(v) it is easily maintained and dissipated for community purpose.
So,Penicillin > Biogas > Curd > Citric acid.

15. How do biofertilizers enrich the fertility of the soil?
Ans: Biofertilizers enrich the fertility of the soil by:
(i) replenishment of lost nutrients like N2, phosphorus, iron, sulphur.
(ii) addition of required micronutrients and macronutrients.
(iii) making humus acid compost.
(iv) acting as scavanger.

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